GNU bug report logs - #73627
29.3; window-main-window: Discrepancy between behaviour and docstring

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Message #8 received at 73627 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: "Nussbaum Ferdinand" <ferdinand.nussbaum <at> inf.ethz.ch>,
 martin rudalics <rudalics <at> gmx.at>
Cc: 73627 <at> debbugs.gnu.org
Subject: Re: bug#73627: 29.3;
 window-main-window: Discrepancy between behaviour and docstring
Date: Sat, 05 Oct 2024 14:15:26 +0300

> From: "Nussbaum  Ferdinand" <ferdinand.nussbaum <at> inf.ethz.ch>
> Date: Fri, 4 Oct 2024 15:09:18 +0000
> 
> To reproduce from emacs -Q, evaluate in the scratch buffer:
> 
> (display-buffer-in-side-window
>   (get-scratch-buffer-create)
>   '((side . left)))
> (split-window (frame-root-window) nil 'below)
> (window-main-window)
> 
> Observe that (window-main-window) returns the selected window. However, the
> window that was created by splitting below is not a side window, and it does not
> descend from the selected window. This contradicts part of the docstring of
> window-main-window:
> 
> "If FRAME has no side windows, return FRAME's root window. Otherwise, return
> either an internal non-side window such that all other non-side windows on FRAME
> descend from it, or the single live non-side window of FRAME."
> 
> Splitting a frame's root window in the presence of side windows seems to often
> lead to such discrepancies. I have observed such behaviour in the packages hydra
> (on ELPA, in its lv-window function), and shell-pop (from another package
> archive).
> 
> Related to that: Is the following supposed to be an invariant for each frame,
> and should it be considered a bug when packages violate it?
> 
> Invariant:
> There exists a window MAIN such that for all live windows WIN (other than MAIN)
> we have: WIN descends from MAIN if and only if it is not a side window.
> 
> This is something I assumed and was surprised to see violated.

Martin, any comments?

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